The present invention relates to a protection of web contents transmitted through a Web-based network, and more particularly relates to a method of and a system for protecting Web contents by using a digital watermark.
Nowadays, a presentation form of a digital content (hereinafter referred to as simply “content”) which is called Webcast (Webcast: Web broadcasting) using a network as broadcasting media, accompanying technical improvement as well as development of infrastructure in the Web-based network such as Internet, is coming into wide use. (By the way, there is no distinctive definition of the term “Webcast”. Sometimes, however, the term is widely used for video distribution, audio distribution, simultaneous distribution of them and on-demand distribution, or combination and synchronization of different digital media, for example, those of a video and an audio with a static image and an animation image and so forth. However, in the present patent specification, it is to be noted that the term Webcast is used as the meaning of the one in which a plurality of types of digital media such as the video, the audio and the static image and so forth are rendered, taking synchronization among them on a browser). In the Webcast, the contents which is composed of a plurality of different types of digital media such as video, audio and static images and so forth are frequently transmitted, and there conventionally exists various tools to develop the contents composed of such plurality of different kinds of digital media (See, for example, “PowerPoint 2003 AddIn:    Microsoft Producer for Microsoft Office Power Point 2003”, [online], Microsoft, [on Aug. 27, 2004, search conducted],    Internet<URL:http://www.microsoft.com/downloads/details.asp x?FamilyID=1b3c76d5-fc75-4f99-94bc-784919468e73&DisplayLang =ja>, and;    “Homepage Builder e-Learning teaching materials making extension”, [online], IBM Japan, [Aug. 27, 2004, search conducted],    Internet<URL:http://www-6.ibm.com/jp/software/internet/hpb/hpbe1.html>). Generally, each of the digital media composing such kind of contents is distributed by the different types of servers such as streaming server and HTTP server, and is rendered as a unified content after synthesized on the Web browser installed in the receiving terminal.
At this stage, in the Webcast, it is sometimes requested that a control is conducted so as not to enable all of users to get all of audio-visual contents but to enable a limited part of the users to get only a limited part of the contents. To realize such controlling, there has been provided one conventional measures in which a portion of digital media such like video, static image, audio and so forth can be hidden by means of the digital watermark (See, for example, Japanese Published Unexamined Patent Publication (Kokai) No. 2000-184177). The digital watermark technology is the one in which the various kinds of information is embedded in the contents by processing the original data of the contents, and is used for the purpose of protecting a copyright and the like. There are two kinds of digital watermarks, i.e., a visible digital watermark that a viewer can recognize and an invisible digital watermark that a viewer cannot usually recognize.
The visible digital watermark to be embedded can be freely selected from various types ranging from one at a high degree in which all of the original still image and video is made virtually invisible (strong visible digital watermark) to a one at a low degree in which the original image and video are almost not influenced (weak visible digital watermark). Due to such feature of the visible digital watermark, for example, the weak visible digital watermark may be embedded in a specified scene of the contents for a promotion purpose and advertisement purpose. In this case, a user is able to watch and listen to the scene with the weak visible digital watermark in quality of image close to the original image quality. Even so, if any illegal use of the image contained in the scene occurs, such usage can be found at a glance by perceiving such weak visible digital watermark. An operation is required to remove the digital watermark by using a dedicated software while providing, for instance, a correct password and key data to thereby render the original image and audio of the contents in which the visible digital watermark is embedded. On the other hand, the invisible digital watermark cannot usually be perceived by a viewer when the contents is rendered, and therefore, a content that does not seem to have any difference in its quality as compared to the image and audio of the original contents with no digital watermark embedded therein is rendered. Nevertheless, the information embedded as the digital watermark in the contents can be extracted through a data processing and accordingly, the invisible digital watermark may be used to find an illegal usage of the contents by detecting the watermark.
Hence, it is possible to provide such a control that a part or all of the video and audio in the contents is hidden by applying the visible digital watermark to the digital media in the contents distributed by Webcast and as a result, only specified users or viewers can remove the visible digital watermark and watch and listen to the original video and audio.